RU2276334C1 - Radiowave level meter - Google Patents

Abstract

FIELD: measuring engineering.

SUBSTANCE: radiowave level meter comprises microwave generator with linear frequency of modulation, receiver of the reflected signal, aerial-feeder path, converter of linear polarization into the circular one, and aerial for emitting and receiving the reflected signal. The aerial-feeder path consists of coaxial wave guide adapter defined by shorted section of the wave guide from one side and two coaxial probes whose axes are mutual perpendicular and are perpendicular to the axis of the wave guide. The cross-section of the wave guide of the coaxial wave guide adapter is cross-shaped. The ratio of the minimum distance between the opposite walls to the maximum distance between the opposite walls ranges from 0.6 to 0.7.

EFFECT: decreased error of measurements.

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Description

The invention relates to techniques for monitoring and measuring the level of liquid and bulk solids.

Known radio wave level meters - pulsed [1, p. 94], the probing signal of which is a short radio pulse, the distance is estimated by the time it takes to reach the surface of the medium and back.

To measure distances not exceeding several tens of meters (the range characteristic of level measurement at technological objects) probing pulses with a duration of not more than tenths of a nanosecond are necessary. At the same time, the requirements for low-frequency components of the device sharply increase, and the use of these meters does not lead to satisfactory accuracy results.

Known as a prototype of a radio wave level meter using linear frequency modulation of a microwave signal [1, p. 95], containing a microwave generator with linear frequency modulation, a reflected signal receiver, antenna-feeder path, as well as radiation antenna and receiving the reflected signal, where the frequency of the reflected signal differs from the frequency of the signal of the generator due to a time delay and the distance measurement is reduced to measuring the beat frequency of two signals, while the measurement accuracy increases with increasing frequency deviation.

When using one antenna for emission and reception of electromagnetic waves, the incident and reflected waves are transmitted along the same waveguide. To separate them, the polarization principle is often used, which is implemented in a circular waveguide and in which both waves are linearly polarized in mutually perpendicular planes [2]. In this case, one of the probes (Fig. IX.74) connected to a microwave generator excites a vertical polarized wave H ₁₁ in a circular waveguide. The converter converts the linear polarization into a circularly polarized wave emitted by the antenna. The wave reflected from the target, passing in the opposite direction of the antenna and the polarizer, will again be linearly polarized, but in the horizontal plane and through another probe it enters the receiver of the reflected signal. Thus, the probes are isolated, that is, a powerful signal from the generator does not directly enter the receiver of the reflected signal, but only after reflection from the target. The foregoing is true so far only a wave of the main type H ₁₁ propagates in the waveguide. When conditions arise in the waveguide for the propagation of one or more higher types of waves, the distribution pattern of the fields in the waveguide changes dramatically, the device becomes inoperative.

Theoretically, the single-wave mode of operation of any waveguide lies between the critical wavelength of the main type λ _{cr 0} and the critical wavelength of the nearest higher type λ _{cr 1} .

In practice, it is impossible to work near critical waves due to a sharp deterioration in the characteristics of any waveguide devices and the operating range lies within:

for a circular waveguide, _{λcr 0} = 1.706d (where d is the diameter of the waveguide), and _λcr.1 = 1.3 06d and based on criterion (1), the working range of the circular waveguide is limited to one point λ = 1.37d, which is significant limits the permissible frequency deviation and ultimately increases the level measurement error.

The objective of the invention is to reduce the error of level measurement by increasing the broadband waveguide path.

The technical result is achieved by the fact that in a radio wave liquid level meter containing a microwave frequency generator with linear frequency modulation, a reflected signal receiver, an antenna-feeder path, consisting of a coaxial-waveguide junction formed by a short-circuited segment of the waveguide and two coaxial probes whose axes are perpendicular to each other and to the axis of the waveguide, the linear to circular polarization transducer, and also the radiation and reception antennas of the reflected signal ala, unlike the conventional waveguide coaxial-waveguide transition is made cruciform cross section with a ratio of the distance between opposite walls remote least to the distance between the outermost opposed walls lying in the range 0.6 ÷ 0.7.

Replacing a circular waveguide with a cross-shaped one with the proposed ratio of the distance between the least distant opposite walls α to the distance with the most distant opposite walls L, lying in the range 0.6 ÷ 0.7, allows increasing the broadband of the wave path, which in turn allows increasing the frequency deviation and, accordingly, reduces the error of level measurement.

The essence of the invention is illustrated in figures 1-4, which show:

figure 1 is a block diagram of the inventive radio wave liquid level meter;

figure 2 - diagram of the antenna-feeder path;

figure 3 is a section along the arrow aa;

figure 4 - dependence of the broadband waveguide on the aspect ratio.

The radio wave liquid level meter contains a microwave frequency generator 1 with linear frequency modulation, an antenna-feeder path, consisting of a coaxial waveguide transition 2, formed by a short-circuited segment of the waveguide and two coaxial probes 3, 4, whose axes are perpendicular to each other and to the axis waveguide, linear to circular polarization converter 5, antenna 6 for radiation and reception of the reflected signal, and also a receiver of the reflected signal 7.

In contrast to the known in the proposed radio wave liquid level meter, the coaxial waveguide transition waveguide is made in cross-section with the ratio of the distance between the least distant opposite walls to the distance of the most distant opposite walls, lying within 0.6 ÷ 0.7.

Microwave generator 1 is a source of microwave oscillations, the frequency of which varies linearly, and can be performed on HMC385LP4 Hittite Microwave Corp. Coaxial waveguide transition 2 consists of a segment of a cross-sectional waveguide and two probes 3 and 4 oriented perpendicular to each other and to the axis of the waveguide.

When a microwave generator 1 signal is applied to one of the probes 3, oscillations with vertical polarization are excited in the waveguide, which do not excite the other probe 4 due to orthogonality. The linearly polarized signal is fed to the polarizer 5, at the output of which we obtain a circularly polarized wave emitted by the antenna 6 into space, for example, into a container partially filled with matter.

The circular polarization signal reflected from the air-liquid interface enters the same antenna 6, then to the linear polarization transducer 5, where it is converted to a linearly polarized wave, but already in the horizontal plane, so the reflected signal excites a microwave probe generator.

In the receiver of the reflected signal 7, which can be performed on the HMC220MS8 Hittite Microwave Corp microcircuit, the signal is mixed with a part of the signal of the microwave generator 1 and in the mixer of the receiver of the reflected signal 7 a difference frequency is allocated proportional to the delay time, proportional to the delay time of the reflected signal and carrying information about the measured fluid level. The measurement error substantially depends on the frequency deviation, i.e., on the broadband of the antenna-feeder path, in particular on the coaxial waveguide transition, which can, in principle, excite higher types of waves if the dimensions of the waveguide allow their propagation.

The choice of a certain ratio of waveguide sizes can provide a single-wave mode of operation in a fairly wide frequency band. Figure 4 shows a graph of the dependence of the overlap coefficient q = λ _{cr 0} / λ _{cr 1} , characterizing the broadband waveguide on the ratio of its sizes, which shows that the proposed replacement of a circular waveguide cross-shaped with an aspect ratio of α / L within 0.6 ÷ 0.7 gives an overlap coefficient q of 1.56. For the working wave range, taking into account the constraint (1), the overlap coefficient q _slave 1.19, i.e. operation in the 19% band is possible, which allows for a small error.

Literature

1. V.A. Viktorov, B.V. Lunkin, A.S. Savlukov "Radio wave measurements of technological process parameters". - M .: Energoatomizdat, 1989, p. 99.

2. Southworth. "Principles and applications of waveguide transmission." Sov.radio, 1955, cc. 362, 363.

Claims (1)

A radio wave liquid level meter containing a linear frequency modulated microwave generator, a reflected signal receiver, an antenna-feeder path, consisting of a coaxial waveguide transition formed by a short-circuited segment of the waveguide and two coaxial probes whose axes are perpendicular to each other and the axis a waveguide, a linear to circular polarization converter, as well as an antenna for radiation and reception of a reflected signal, characterized in that the waveguide is a coaxial waveguide transition is formed with a cruciform cross-section ratio of the distance between opposite walls remote least to the distance between the outermost opposed walls lying in the range 0.6 ÷ 0.7.

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